Herpesvirus capsids assemble in the nucleus, while final virion maturation proceeds in the cytoplasm. This requires that newly formed nucleocapsids cross the nuclear envelope (NE), which occurs by budding at the inner nuclear membrane (INM), release of the primary enveloped virion into the perinuclear space (PNS), and subsequent rapid fusion with the outer nuclear membrane (ONM). During this process, the NE remains intact, even at late stages of infection. In addition, the spacing between the INM and ONM is maintained, as is that between the primary virion envelope and nuclear membranes. The linker of nucleoskeleton and cytoskeleton (LINC) complex consists of INM proteins with a luminal SUN (Sad1/UNC-84 homology) domain connected to ONM proteins with a KASH (Klarsicht, ANC-1, SYNE homology) domain and is thought to be responsible for spacing the nuclear membranes. To investigate the role of the LINC complex during herpesvirus infection, we generated cell lines constitutively expressing dominant negative (dn) forms of SUN1 and SUN2. Ultrastructural analyses revealed a significant expansion of the PNS and the contiguous intracytoplasmic lumen, most likely representing endoplasmic reticulum (ER), especially in cells expressing dn-SUN2. After infection, primary virions accumulated in these expanded luminal regions, also very distant from the nucleus. The importance of the LINC complex was also confirmed by reduced progeny virus titers in cells expressing dn-SUN2. These data show that the intact LINC complex is required for efficient nuclear egress of herpesviruses, likely acting to promote fusion of primary enveloped virions with the ONM.

IMPORTANCE While the viral factors for primary envelopment of nucleocapsids at the inner nuclear membrane are known to the point of high-resolution structures, the roles of cellular components and regulators remain enigmatic. Furthermore, the machinery responsible for fusion with the outer nuclear membrane is unsolved. We show here that dominant negative SUN2 interferes with efficient herpesvirus nuclear egress, apparently by interfering with fusion between the primary virion envelope and outer nuclear membrane. This identifies a new cellular component important for viral egress and implicates LINC complex integrity in nonconventional nuclear membrane trafficking.

疱疹病毒衣壳在细胞核中聚集，而最终的病毒粒子成熟则在细胞质中进行。这就要求新形成的核衣壳穿过核被膜（NE），这是通过在内核膜（INM）上萌芽，将初级被包裹的病毒体释放到核周空间（PNS）中以及随后与外核膜的快速融合而发生的。 （ONM）。在此过程中，即使在感染后期，NE仍保持完好无损。此外，INM和ONM之间的间隔也保持不变，主要病毒体包膜和核膜之间也保持间隔。核骨架和细胞骨架（LINC）复合体的连接体由具有管腔SUN（Sad1 / UNC-84同源性）结构域的INM蛋白与具有KASH（Klarsicht，ANC-1，SYNE同源性）域，并被认为是造成核膜间距的原因。为了调查LINC复合体在疱疹病毒感染期间的作用，我们生成了组成型表达SUN1和SUN2的显性负（dn）形式的细胞系。超微结构分析显示，PNS和连续的胞浆内腔显着扩展，最有可能代表内质网（ER），尤其是在表达dn-SUN2的细胞中。感染后，初级病毒体积聚在这些扩大的腔区域中，也离细胞核很远。LINC复合物的重要性还通过降低表达dn-SUN2的细胞中的子代病毒滴度来证实。这些数据表明完整的LINC复合物是疱疹病毒有效核扩散所必需的，

重要信息虽然在高分辨率结构方面已知内核膜上主要包裹核衣壳的病毒因素，但细胞成分和调节剂的作用仍然是未知的。此外，负责与外核膜融合的机制尚未解决。我们在这里显示，显性负SUN2干扰有效的疱疹病毒核出口，显然是通过干扰主要病毒粒子包膜和外核膜之间的融合。这确定了对于病毒出口重要的新的细胞成分，并暗示非常规核膜运输中的LINC复合物完整性。